Another two titles have joined the ever expanding Xbox Backward Compatibility program, including Sonic Adventure 2
and Earth Defense Force 2017
Sonic Adventure 2
In Sonic Adventure™ 2, will you choose to save the world or conquer it? The hunt for the Chaos Emeralds is on and battle lines have been drawn between Hero and Dark. Experience two unique adventures featuring both long-time heroes and new and returning villains as they battle for the fate of the world!
Earth Defense Force 2017
2013 AD: A radio transmission is intercepted from an unknown extraterrestrial source 2014 AD: Attempts are made to establish contact with the source, but to no avail. 2015 AD: A technologically advanced international army, the EDF, is established. 2017 AD: A large fleet of alien spaceships, dubbed the Ravagers, arrives on Earth and begins indiscriminately attacking humans... "Earth Defense Force" is a shooting action game and follow-up to "THE Earth Defense Force" and "THE Earth Defense Force
As always, you can find the complete list of backward compatible games here